Another factor to be considered is the charge-transfer energy \(E_d\) , the energy deviation between Cu 3\(d\)  (UH) and O2\(p\)  (or ZR) energy levels. A previous doping-dependent ARPES study on NCCO manifested the spectral weight transfer from the Cu3\(d\) -O2\(p\)  hybridized Zhang-Rice band to the quasiparticle state [1]}. The study points out that the \(N_{\mathrm {eff}}\) /Cu of cuprates can be mainly determined by either or both \(U/t\)  and \(E_d/t\) . Another recent comparative study on the effective correlation strength \(U/t\)  and the effective charge-transfer energy \(E_d/t\)  revealed an intriguing qualitative difference between \(U/t\)  and \(E_d/t\)  [2]}. In more detail, as the atomic number of rare-earth in the electron-doped cuprates decreases from Sm to Pr, the \(U/t\)  decreases whereas the \(E_d/t\)  increases. As a result, the smaller atomic number makes \(U/t\)  (\(E_d/t\) ) farther from (closer to) that of La\(_2\) CuO\(_4\) , the parent compound of LSCO. Considering that PLCCO has the longest Cu-O bonding length with the smallest rare-earth atomic number among the bulk electron-doped families, the small \(N_{\mathrm {eff}}\) /Cu with the low cutoff energy of PLCCO, which is comparable with that of LSCO rather than NCCO, suggests that \(E_d/t\) , instead of \(U/t\) , is likely the main determinant of the spectral weight transfer in doped cuprates.
